Update README.md

Documentation for FlipbookUV node.

README.md

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 # Godot-Shader-Lib
 Visual shader node library for Godot engine.
+
+Adds various extra nodes to use in built-in visual shader editor.
+## Installation
+Copy the contents of **_addons/ShaderLib_** into the same folder in your project. No activation needed. Custom visual shader nodes work the same way as standart visual shader nodes.
+## Uninstallation
+Delete the contents of **_addons/ShaderLib_** folder from your project. Make sure to delete it using the Godot editor instead of your default file system program.
+## Nodes documentation
+### UV nodes
+___
+#### Flipbook uv node
+Creates a flipbook, or texture sheet animation, of the UVs supplied to input UV. The amount of tiles on the sheet are defined by the values of the inputs **_rows_** and **_columns_**.
+This node can be used to create a texture animation functionality, commonly used for particle effects and sprites, by supplying Time to the input Tile and outputting to the UV input slot of a Texture Sampler.
+
+**Inputs**
+|Name|Type|Binding|Description|
+|---|---|---|---|
+|uv|vec2|UV|Input UV value|
+|rows|int|none|Amount of horizontal tiles in texture sheet|
+|columns|int|none|Amount of vertical tiles in texture sheet|
+|start frame|int|none|Start tile index texture sheet|
+|end frame|int|none|End tile index texture sheet|
+|anim speed|float|none|Animation speed|
+
+**Outputs**
+|Name|Type|Binding|Description|
+|---|---|---|---|
+|uv|vec2|None|Output UV value|
+___